A. Field of the Invention
The invention relates generally to a servo activated shutter mechanism and, more particularly, to a servo activated shutter mechanism adapted for use in can manufacturing.
B. Description of the Related Art
Manufacturing cans requires a large number of forming and machining operations. For example, fabrication of a two-piece beverage can may require two dozen or more separate necking, ironing, trimming, washing, decorating and spraying operations. Typically, these operations are performed in a series of modules by function. In any one of these operations, a can may be damaged and rendered unusable. If damaged, the can should be removed from the line to reduce the cost of manufacturing. Some processes include a mechanism to discharge such cans from the machine.
Prior to palletizing cans for shipment, all cans are individually inspected for pin holes, split flanges, split domes and other perforations. Some conventional systems use a light sensor. With the open end of the can seated and sealed up to the light sensor, the outside of the can is flooded with light. If there is a hole in the can, light will be admitted into the can and will be detected by the sensor. Thus, damaged cans can be identified and removed from the can-making line.
One conventional system uses a stand alone test machine after the final forming module. Cans are fed by traditional trackwork. Although this system works, each stand alone test machine requires a separate drive, control panel, conveyance and line controls. This adds a considerable cost to the manufacturing line.
Another conventional system, the positive transfer inspection machine, uses infeed and exit starwheels rather than traditional trackwork to feed and remove cans from the final forming modules. This system has the advantage that the light sensor is integrated into the module, obviating the need for the extra equipment required for the stand alone test machine.
Although more cost effective than the stand alone test machine, the positive transfer inspection machine has an inherent process drawback. It works well as long as there is a can in the pocket of the starwheel. However, if a can has already been removed from the upstream process (e.g. damaged can fallout), the sensor is exposed to an empty pocket. Therefore, the sensor is exposed to significantly more light than it is designed for. This results in the sensor being temporarily blinded. This is similar to what happens to the human eye when an individual is awakened at night from an overhead light. Typically, in the time it takes for the sensor to return to normal operation, as many as three cans or more may have passed by the sensor and be classified as having defects while in reality they may have been acceptable.
An empty pocket can be recognized in advance of the pocket reaching the light sensor by virtue of a proximity sensor. With the usage of an encoder or resolver, the time or position at which the pocket reaches the light sensor can be determined. However, the present state of light sensor technology does not allow the light sensor to xe2x80x9cturn offxe2x80x9d or xe2x80x9cdecayxe2x80x9d fast enough relative to the upcoming adjacent empty pocket.
The required delay time is determined primarily by the machine speed and pocket-to-pocket pitch of the starwheels. A fast speed and small pitch combination on a positive transfer machine necessitates very fast decay times. However, current state of the art light sensors have decay times which are relatively slow, too slow for such combinations.
Thus, the prior art light testing apparatuses are easily blinded and are unsuitable for the rejection of defective cans in high speed positive transfer can manufacturing lines. Therefore, it would be desirable to have a light testing apparatus which is not easily blinded and acceptable for use in modern high speed can manufacturing.
The present invention includes a servo-shutter mechanism comprising a servo-motor, a first gear rotatably attached to the servo-motor, the gear having teeth, a second gear having a first end and a second end, the first end having teeth in meshing contact with the teeth of the first gear, and the second end adapted to be joined to a cam ring, a cam ring having an aperture and a plurality of pivot pins, one of the pivot pins joined to the second end of the second gear and at least one shutter blade having a first end and a second end, the first end adapted to be pivotably joined to the cam ring, the second end adapted to block the aperture.
The present invention also includes a light testing apparatus comprising a servo-motor, a first gear rotatably attached to the servo-motor, the gear having teeth, a second gear having a first end and a second end, the first end having teeth in meshing contact with the teeth of the first gear, the second end adapted to be joined to a cam a cam ring having an aperture and a plurality of pivot pins, one of said pivot pins joined to the second end of the second gear at least one shutter blade having a first end and a second end, the first end adapted to be pivotably joined to the cam ring, the second end adapted to block the aperture, a pin hole in the at least one shutter blade, the pin hole adapted to admit a predetermined amount of light, a light source adapted to shine light onto a container and a light sensor adapted to detect the predetermined light.
Additionally, the present invention includes a method of testing a can for defects comprising the steps of conveying the can to a light detecting apparatus, the apparatus including a servo-motor, a first gear rotatably attached to the servo-motor, the gear having teeth, a second gear having a first end and a second end, the first end having teeth in meshing contact with the teeth of the first gear and the second end adapted to be joined to a cam ring, the cam ring having an aperture and a plurality of pivot pins, one of said pivot pins joined to the second end of the second gear and at least one shutter blade having a first end and a second end, the first end adapted to be pivotably joined to the cam ring, the second end adapted to block the aperture, shining light onto the can and detecting light from the can with the light detecting mechanism.
The present invention also includes a method for testing cans for defects comprising the steps of determining if a pocket in a can conveying apparatus is empty, substantially preventing light from a light source from impinging on a light sensor if the pocket is empty and if the pocket is full, opening a path capable of allowing light from the light source to the light sensor. The step of determining if a pocket in a can conveying apparatus is empty may be done with a proximity sensor.